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View Full Version : Steel frame for 8' * 4' cnc bed ?



flanagaj
12-10-2011, 08:41 PM
Hi,

I am in the process of designing the bed for my CNC machine and would appreciate any guidance regarding frame dimensions and material choice.

My plan is to weld a steel frame together with 10mm * 50mm plate welded to the sides of the upper rails, which will then be milled by a local machine company in readiness to accept the linear guide rails. They have quoted 800 to mill the side rails and drill all of the holes.

Their machine is super accurate and will ensure that the rails are 100% parallel and level to each other, resulting in super accuracy. Whilst 800 is expensive it will save me the headache of getting the rails aligned

My plan is to base it on the axyz 4000 series machine as shown below.

4739

JAZZCNC
12-10-2011, 11:02 PM
First can I ask the main intended use.?

flanagaj
12-10-2011, 11:42 PM
First can I ask the main intended use.?The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.

I don't want to use aluminium profile section as I think those machines have poor resale if you ever decide to build another one.

Do you have any suggestions that might be of help ?

Thanks

Jonathan
13-10-2011, 01:53 AM
The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.

If it's mainly for wood then that sort of accuracy is not going to make an appreciable difference. 800 sounds a lot ... invest it in profile rails etc. How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.

Getting the rails parallel is not a problem - once you have the gantry mounted and put a couple of bolts in one rail the other will self align. Either that or you can use a DTI to align them by affixing it to one carrage with the needle against the other rail.

Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.

flanagaj
13-10-2011, 07:16 AM
How can you be sure that after the frame has been machined when you fix it to the floor it does not distort. I too did think about this and came to the conclusion that as the machine is to be made from pretty substantial material it will not be able to distort. Do the large professional cnc machines get aligned up on site when they are delivered ?


Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy. I have read about this, but never did find out where the "right type of epoxy" can be sourced.

I don't want the machine bolted to the floor, I just want it to sit on the levelled feet.

Do you think that once a frame is constructed from 80mm * 80mm * 6mm box section and then machined it will still be able to distort ?

Web Goblin
13-10-2011, 08:32 AM
80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

Ian

Karl
13-10-2011, 11:28 AM
We would certainly be interested in hearing the personal experiences of anyone who's used epoxy et al to level the top rails of a larger frame. Our Mark-3 machine will be for 8' x 4' sheets. (That said, we're still assembling the bits for MK-2).

Karl

flanagaj
13-10-2011, 01:36 PM
80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

Ian Do you think that is over sized ?

Jonathan
13-10-2011, 01:56 PM
80 x 80 x 6 box section can still distort.

Yep, anything will distort. It's a matter of how much and the effect it has.

Heavy frame = good, as long as you don't have to move it!

For a machine purely for woods it does seem a bit excessive, however you seem to want to use it for milling aluminium too in which case it pays to make it as strong as you can.

What sort of tolerances do you require as that it what determines if machining the rail surfaces perfectly parallel is necessary? You can compensate for it perfectly well in software.

flanagaj
13-10-2011, 04:50 PM
Yep, anything will distort. It's a matter of how much and the effect it has.

Heavy frame = good, as long as you don't have to move it!

For a machine purely for woods it does seem a bit excessive, however you seem to want to use it for milling aluminium too in which case it pays to make it as strong as you can.

What sort of tolerances do you require as that it what determines if machining the rail surfaces perfectly parallel is necessary? You can compensate for it perfectly well in software.Ideally, I would like to have an accuracy of at least 0.05mm. Worst case scenario I could stretch to 0.1mm, but no worse

JAZZCNC
13-10-2011, 06:12 PM
Hi Ian,

Completely agree it's not neccesory to spend 800 to get the machine you want.

Regards your question of do they setup professional machines on site then yes they do and to a very high degree taking a great deal of time using very costly precision levels etc, also they are bolted to the floor more often than not on shock dampening feet.

Obviously good build quality is required but Setting up the machine while in situ is the key to an accurate machine, time taken here will make or break the machine.
The heavist machines built from quality cast iron still bend and twist requiring carefull leveling and setup so don't think for one second 80x80 is substantial and won't move or require setup.!. . . In real machine terms it's banna material.!!

Also regards Epoxy, Yes it will self level to a high degree but it still requires the machine to be fixed and levelled to high degree before application and will only be accurately level to that one spot.

Basicly what I'm saying is if you want good accurecy then Yes 80x80 will do what you want it to do and with good build quality and attention to detail will give the accurecy you require but the machine needs to be fixed down with adjustment built into the design.

If good strong design with carefull welding and attention to detail is used, mixed with very carefull setup then you will easily surpass the accurecy you desire without having to spend 800 on surfacing.

800 would be far better spent on using quality components.!!

JAZZCNC
13-10-2011, 06:23 PM
What sort of tolerances do you require as that it what determines if machining the rail surfaces perfectly parallel is necessary? You can compensate for it perfectly well in software.

Oh god here we go again.!!! . . . Don't talk soft you can compensate for un-parallel rails in software.!! . . . How.???

Jonathan I'm not wanting to get into a fight with you again but you are miss-leading folks and plan wrong by promoting software can compensate for poor build quality. . . . please stop it because it curdles my noodle. :redface: (And I'll always challenge just for the sake of newcomers.!)

flanagaj
13-10-2011, 06:53 PM
Hi Ian,

Completely agree it's not neccesory to spend 800 to get the machine you want.

Regards your question of do they setup professional machines on site then yes they do and to a very high degree taking a great deal of time using very costly precision levels etc, also they are bolted to the floor more often than not on shock dampening feet.

Obviously good build quality is required but Setting up the machine while in situ is the key to an accurate machine, time taken here will make or break the machine.
The heavist machines built from quality cast iron still bend and twist requiring carefull leveling and setup so don't think for one second 80x80 is substantial and won't move or require setup.!. . . In real machine terms it's banna material.!!

Also regards Epoxy, Yes it will self level to a high degree but it still requires the machine to be fixed and levelled to high degree before application and will only be accurately level to that one spot.

Basicly what I'm saying is if you want good accurecy then Yes 80x80 will do what you want it to do and with good build quality and attention to detail will give the accurecy you require but the machine needs to be fixed down with adjustment built into the design.

If good strong design with carefull welding and attention to detail is used, mixed with very carefull setup then you will easily surpass the accurecy you desire without having to spend 800 on surfacing.

800 would be far better spent on using quality components.!!You have answered a fundamental question for me here. I always thought I could get away with having a meaty frame welded together, sent off to be milled and the linear rails attached to then come back to me on a lorry, into the workshop and straight to work without any further alignment required. You have basically told me that this is not possible, so I need to have a rethink.

I have read the MadVac web site on how he aligned his linear rails and it makes me weep as it seems such a laborious process that seems very hit and miss. I was hoping that I could just pay to have that part of the build done for me.

Web Goblin
14-10-2011, 07:10 AM
Do you think that is over sized ?

No I dont think the material is oversized.
If you want a really sturdy machine then you cant really oversize the frame material, within reason I might add. Box section steel itself isnt really that strong unless you start going into heavy wall thickness stuff and as Jazzcnc has said getting your construction right to start with will make all the difference and would save you 800 on machining.

Ian

Jonathan
14-10-2011, 10:45 AM
Oh god here we go again.!!! . . . Don't talk soft you can compensate for un-parallel rails in software.!! . . . How.???

In mach3 go to "Function Cfg's" then "Formulas". If you can measure the error (dial indicator etc) then it will be possible to work out a forumula to compensate, and eliminate it.

Of course it is better to get it right to start with, for obvious reasons, but if after doing all the things we suggest it turns out that there is a small error or, as is likely with a welded frame, it gradually moves, that's something you can do to compensate. Better than nothing.

Surprised Jazz didn't mention this as he has before ... but to damp resonance on a steel frame you can fill it with sand.

JAZZCNC
14-10-2011, 04:05 PM
In mach3 go to "Function Cfg's" then "Formulas". If you can measure the error (dial indicator etc) then it will be possible to work out a forumula to compensate, and eliminate it.

So whats the formula to get Mach to stop loosen the rails eliminate binding and tighten back down.??? . . . Your talking tosh and again passing on missleading vaguely accurate impracticle information which just sends wrong signals to newcomers who only discover this far into the build when it's too late.!. . . . End result being they can become disspondent and give up.

Much more helpfull to give sound advice encouraging good accurate build quality than saying just build it and don't worrie because software will compensate for your shity work.!!
Software compensation and formulas etc are last ditch work arounds which never work correctly or has desired.!!. . . . .Effectively they are weak bodge's not to be encouraged IMO.

Jonathan
14-10-2011, 05:28 PM
So whats the formula to get Mach to stop loosen the rails eliminate binding and tighten back down.??? . . . Your talking tosh and again

I think you're missing the point I'm making. I said in my last post that obviously it's better to get it right to start with and that software compensation helps if and only if it is a *small* error. I didn't think I needed to state that by small I don't mean binding or tight rails as you'd be foolish to try and run a machine like that for obvious reasons.


Software compensation and formulas etc are last ditch work around

Exactly ... which are better than nothing. If the machine is running smoothly then I see no reason not to use maths to improve it.

No matter how well you build the machine you will never get all axis perfectly true and perpendicular. The best you can get is the error being negligible compared to the tool deflection. If it's only just over negligible then the machine may well run smoothly and if so you can use the formulas to compensate.


Much more helpfull to give sound advice encouraging good accurate build quality than saying just build it and don't worrie because software will compensate

I thought I did say that in my previous posts ('it is better to get it right to start with') on this thread. If not I'll not bother.

blackburn mark
14-10-2011, 06:31 PM
Oh god here we go again.!!! . . . Don't talk soft you can compensate for un-parallel rails in software.!! . . . How.???




In mach3 go to "Function Cfg's" then "Formulas". If you can measure the error (dial indicator etc) then it will be possible to work out a forumula to compensate, and eliminate it.




So whats the formula to get Mach to stop loosen the rails eliminate binding and tighten back down.???


i think you changed aurguments there jazz, its unfair of you to talk like your "THE MAN" when your not man enough to admit that you were unaware of mach's ability to compensate..... surly it would be better for you and the rest of us if you had said
"sh*t... how the hell do you do that?" then you me and all the uninitiated you keep going on about might learn some brand new shit :smile:

JAZZCNC
15-10-2011, 01:18 AM
i think you changed aurguments there jazz, its unfair of you to talk like your "THE MAN" when your not man enough to admit that you were unaware of mach's ability to compensate..... surly it would be better for you and the rest of us if you had said
"sh*t... how the hell do you do that?" then you me and all the uninitiated you keep going on about might learn some brand new shit :smile:

No Mark I'm very much Man enough to admit when I don't know something or indeed I'm plain wrong. . which in this case don't feel I am. . . . I'm also very open to learning new shit, Which I do every day.!!
I also know very well about Mach's compensation features, also know they have very limited affect and difficult to impliment. Even Art fennerty Mach's designer agree's they are unrealiable and only to be used in case's or when all else fails and expect limited success.!!

Know I don't really give a flying F@#K what YOU, Jonathan or anybody else thinks about my comments. . . . I do care that people should be mindfull that newbie's will be reading and soaking up these missleading post's and it can and does cost people valuable time and money, even leading to discourageing them to try again when it doesn't perform as expected.

My comments are not in anyway personal to Jonathan, believe me I would be them same regardless who it was and will always challenge information I feel is wrong or missleading.

Not every one likes posting on forums, I know from experience helping those that have had the good sense or courage to ask for help that this is particularly true in both the young and older generations.
They sit back and prefer to skim post's soaking up information both good and bad like sponges, they latch onto anything that seems to fit the bill for there particular needs or requirements.
Comments inferring software can compensate for less than ideal build quality along with other urban cnc myth's like bigger, faster is better etc are latched onto and implimented into first time builds often with disasterous expensive results.

All I'm asking is that influential posters consider what they post and instead of trivialising the need for care while building and they promote and emphasise the advantage good build practice makes instead.!

Jonathan I'm Sorry if I've up set you and know your comments are ment with the best of intentions but I feel you really do need to be more mindfull new people will be reading your post's. A bit more explination and clarification of the short comings of some the suggestions would be more helpfull.

Now with that said I don't want this to escalate any further as it's distracting and not fair to the original posters thread.! . . . For this I do appologise to Justin because I was the one who jumped on Jonathan and started it all but please let's leave it here.!! . . . . . If you feel you must rebuff me then please feel free to PM me.!

blackburn mark
15-10-2011, 02:15 AM
jazz, maybe in future "you" will be more mindful and PM the people that you want to tare a strip from... besides that i think we are all open to critisism if its unagressive and done without an air of superiority.

i also appologise Justin for my part in hijacking this thread.

JAZZCNC
15-10-2011, 03:08 AM
jazz, maybe in future "you" will be more mindful and PM the people that you want to tare a strip from... besides that i think we are all open to critisism if its unagressive and done without an air of superiority.

i also appologise Justin for my part in hijacking this thread.

Ok Mark, first I didn't tare strips and neither was I aggresive. Also I can't help it if you take confidense gained with experience and twist it into something else like superiosity.

Thou I will take your critisism on board and if feel the need directly PM folks warning of bullshit posters.:thumbdown:

I'm leaving it here now. . good night.!

Colin Barron
15-10-2011, 08:24 PM
If you are not bothered about weight, why don't you buy an old machine and fit new drives and electronics. i would have thought you are more likely to achieve the level of accuracy you require.

flanagaj
17-10-2011, 07:19 AM
If you are not bothered about weight, why don't you buy an old machine and fit new drives and electronics. i would have thought you are more likely to achieve the level of accuracy you require. I have trawled in the interweb for hours on end looking for 2nd hand cnc machines, and not had a great deal of joy.

Colin Barron
17-10-2011, 07:01 PM
what about this: http://www.ebay.co.uk/itm/Wadkin-UX-LCC3-CNC-Router-/150668158563?pt=UK_BOI_Building_Materials_Supplies _Carpentry_Woodwork_ET&hash=item231485a663

flanagaj
18-10-2011, 09:57 PM
what about this: http://www.ebay.co.uk/itm/Wadkin-UX-LCC3-CNC-Router-/150668158563?pt=UK_BOI_Building_Materials_Supplies _Carpentry_Woodwork_ET&hash=item231485a663
That is slightly too large. I have another plan in progress which is to make the base out of concrete and the rails out of epoxy granite and all so that it can be dismantled easily.